The present invention is concerned with methods and equipment for diagnostic tests of the eyes, and more particularly, with an automatic system for examination of the field of vision of a patient. The system is mounted on a head set and is equipped to continuously track eye movement so as to focally project a spot of retinal threshold-related light stimuli on preselected retinal areas, regardless of the direction of the gaze of the patient or of the orientation of the head of the patient. The system can concomitantly measure the pupil size and intensity of light reflected through the pupil as a result of the light projected.
The examination of the field of vision of a patient is an extremely important diagnostic tool used to identify and analyze diseases and defects of the retina and as visual pathways, such as glaucoma, optic neuropathy, multiple sclerosis and compression of the visual pathways. In the past, such an examination was performed with manually operated field of vision test instruments known as perimeters. Manually operated perimeters require the services of a physician or a skilled technician in order to examine the patient. In the most widely used system, known as the Goldmann system, the patient must sit still, head clamped in place, and constantly watch a fixation target at the center of a hemispherical screen to eliminate any uncertainties caused by head and eyes movements. A small point of light of varied intensity, size and color is projected onto the screen and its position is varied by the operator. The limits of the visual field are determined on the basis of the manual or verbal indications of the patient as to when the point of light comes into or goes out of view as the light is moved radially between the periphery and the center of his view. The examiner must continuously watch the patient to ascertain that the eye of the patient is fixated on the center of the screens since the examination results are artefactual if the eyes of the patient are not immobile. These factors render the examination of the extent of the field of vision using the commonly available Goldmann system is basically subjective, dependent to a large extent on the skill of the examiner, the fatigue level of the patient and the ability of the examiner to communicate with the patient. Thus, the Goldmann system is not operable for small children and patients who must remain in a supine position.
More recently, automatic perimeters have been marketed and used. However, even these instruments rely upon the Goldmann system and incorporate the control of a microprocessor in order to more efficiently measure the effect of light stimuli from external sources. Other prior art instruments have added a head set or helmet to eliminate any effect of head movements on the final results, as disclosed in United Kingdom Application No. 2096791 and two reports from the IOVS J. Whiteside-Michel et al., "Virtual Reality Visual Field Test.", IOVS/97, 38:4, S569; and L. Brigatti et al., "Virtual Perimetry: A Novel Perinmetric Technique", IOVS/97, 38:4, S572!. Alternatively, various systems have been disclosed which use more objective means for perimetry such as pupillary size determination during Humfrey perimetry, as disclosed in U.S. Pat. No. 5,490,098. U.S. Pat. No. 5,114,222 discloses a method which includes a light stimulus moved in a continuous circular path according to decreased pupillary response. U.S. Pat. No. 5,459,536 discloses an instrument which includes a device to track eye movement, so that such movements can be incorporated into the final analysis of the results. However, all of these instruments and methods perform indirect measurements in which the light stimulus is projected in front of the eyes of the patient, rather than directly stimulating the retinal nerve fibers with fight.
There is thus an unmet medical need for a method and a system which objectively examines the visual field of a patient in which the retinal nerve fibers are directly stimulated by a retinal threshold-related light stimulus, such that the change in pupillary size in response to this light is automatically measured, and such that this measurement is cross-checked by determination of the change in the amount of light reflected from the retina, such that the patient does not need to remain substantially immobile during the examination and such that the method and system can be used to examine patients which must remain supine or who cannot otherwise comply with the requirements of prior art manual perimetry methods.